Noyori Hydrogenation: Aromaticity, Synchronicity, and Activation Strain Analysis

Abstract

By means of density functional theory calculations, we have computationally explored the intimacies of the crucial step of Noyori hydrogrogenation reactions of multiple bonds. This process can be considered analogous to the so-called double group transfer reactions. Both kinds of transformations proceed concertedly via the simultaneous migration of two hydrogen atoms/groups in a pericyclic [σ2s + σ2s + π2s] reaction through six-membered transition structures. Despite the structural resemblances of both types of saddle points, significant differences are found in terms of synchronicity and in-plane aromaticity. In addition, the activation strain model has been used to get quantitative insight into the factors which control the corresponding barrier heights. It is found that the presence of a heteroatom in the acceptor moiety is responsible for a remarkable increase of the interaction energy between the reactants which can compensate the destabilizing effect of the strain energy associated with the deformation of the initial reagents leading to low reaction barriers.

The activation strain model and molecular orbital theory

“…Conveniently, there is no special computer code required to perform activation strain analyses: all necessary quantities can be computed using any of the regular quantum‐chemical software packages available. As a result, the activation strain model has been applied by various research groups, on a range of chemical processes, such as nucleophilic substitution, cycloaddition, oxidative addition, isomerization, and many other processes from organic and organometallic chemistry.…”

autoDIAS: a python tool for an automated distortion/interaction activation strain analysis

“…This analysis can be applied to single geometries or multiple geometries along a scan or reaction coordinate, to provide information on the nature of interaction between the fragments and the potential energy surface. This method has been widely applied for a broad range of chemical systems such as cycloadditions, ene reactions, metal complexes and catalysis, organocatalysis, and addition and substitution reactions …”

“…This analysis can be applied to single geometries or multiple geometries along a scan or reaction coordinate, to provide information on the nature of interaction between the fragments and the potential energy surface. This method has been widely applied for a broad range of chemical systems such as cycloadditions, [6][7][8][9][10][11][12][13][14][15][16][17][18] ene reactions, [19] metal complexes and catalysis, [20][21][22][23][24][25][26][27] organocatalysis, [28][29][30][31] and addition [32] and substitution reactions. [33][34][35] The implementation of a DIAS analysis is straight forward and can be performed using any electronic structure software.…”

Assessing the effective factors affecting the conformational preferences and the early and late transition states of the unimolecular retro-ene decomposition reactions of ethyl cyanate, ethyl thiocyanate and ethyl selenocyanate

“…To gain further insights into the nature and mechanisms of the retro-ene decomposition reactions of compounds 1-3 and the applicability of the Hammond-Leffler postulate in these reactions, we examined their synchronicity indices by calculating the bond orders [total natural resonance theory (NRT) bond orders (natural bond orders, nbo)] of the gauche, transition state, and product structures. [75][76][77][78] The synchronous or asynchronous nature of the mechanisms of the retro-ene decomposition reactions of compounds 1-3 were also considered by the synchronicity, Sy, as calculated from eqn (2):…”